Conditions under which primary mouse embryo cells undergo transformation upon infection with vaccinia virus and become tumorigenic in newborn mice will be investigated. Virus specific transcription and translation products required for cell transformation will be determined. The mechanisms of poxvirus DNA replication will be studied in vivo and in vitro. The nature of the modifications in the host cell membrane after infection with vaccinia virus and Yabapox virus will be studied and compared. The effect of such alterations on cell-to-cell interaction and cell growth will be determined.